Post-seismic motion after 3 Chilean megathrust earthquakes: a clue for a linear asthenospheric viscosity

Abstract

Over the last decade, three major subduction earthquakes, Maule Mw 8.8 (2010), Illapel Mw 8.3 (2015) and Iquique Mw 8.1 (2014), occurred in Chile and generated significant post-seismic deformations. These large scale and long lasting deformations can be quantified with modern GNSS precise positioning and highlight visco-elastic processes in the asthenosphere. Here, we calculate the ratios of cumulative post-seismic displacements after 5 years over the co-seismic offsets. We find that at any distance from the trench, ratios are similar for the three earthquakes despite their different magnitudes which imply induced stresses that are more than one order of magnitude apart. This observation suggests that the post-seismic deformation is related to the same effective viscosity for the three earthquakes, indicating Newtonian rheology, rather than power-law rheology in the asthenosphere.

Return of the Atacama deep Slow Slip Event: The 5-year recurrence confirmed by continuous GPS

“…The tectonic context in Atacama, in the interseismic phase about a century after the latest major earthquake, was favorable to detect the SSE2014 by survey GPS. In contrast, regions like Navidad (34.8°S) or Los Vilos (32°S), where swarms regularly occur, are strongly affected by the postseismic deformations following the 2010 Maule and 2015 Illapel earthquakes [Klein et al, 2016;Boulze et al, 2022]. In such a context, the survey GPS can not compensate for the low density of continuous stations.…”

Frictional Properties and Rheological Structure at the Ecuadorian Subduction Zone Revealed by the Postseismic Deformation Due To the 2016 Mw 7.8 Pedernales (Ecuador) Earthquake

“…Most recently, Boulze et al. (2022) suggested that a mantle viscosity of ∼5 × 10 18 Pa s produced the right order of magnitude of postseismic displacements following the 2014 Iquique and 2015 Illapel events. Based on the absence of time and spatial variation in the ratio of postseismic to coseismic displacements, they argued that a Maxwell viscosity model was preferred to a power law viscosity.…”

“…Over 2010–2015, three subduction earthquakes, Maule M w 8.8, Illapel M w 8.3 and Iquique M w 8.1 occurred in Chile and generated significant postseismic deformation (e.g., Boulze et al., 2022) (Figure 7). Among them, the largest and the most studied event was the 2010 Maule earthquake, central Chile (Bedford et al., 2016; Sun et al., 2018; Weiss et al., 2019).…”

“…For example, Li et al (2018) built a postseismic model with spatiotemporally varied Maxwell viscosities based on the GPS data 8 years after the Maule event after removing the afterslip model of Bedford et al (2016). When the thickness of the elastic layer was fixed to 45-50 km, the optimal viscosities along the south Chile subduction zone Most recently, Boulze et al (2022) suggested that a mantle viscosity of ∼5 × 10 18 Pa s produced the right order of magnitude of postseismic displacements following the 2014 Iquique and 2015 Illapel events. Based on the absence of time and spatial variation in the ratio of postseismic to coseismic displacements, they argued that a Maxwell viscosity model was preferred to a power law viscosity.…”

Influence of the asthenosphere on earth dynamics and evolution

“…Because PSR studies are generally sensitive to the viscosity of the uppermost sublithospheric mantle (perhaps only ~ 10 km or so), these low values are not inconsistent in any obvious way with, e.g., the Fennoscandian rebound results discussed above, as per the restrictions implied by the Ct scaling. Also, Boulze et al 28 have recently concluded that the asthenosphere responds to large subduction zone earthquakes via linear (Newtonian) rheology, as opposed to power-law rheology.…”